The correct answer is: c. Resurgence of militant nationalism and populism.Regionalism faces various challenges, but the resurgence of militant nationalism and populism is a significant threat. This phenomenon:1. Undermines cooperation: Nationalist ideologies prioritize individual country interests over regional collaboration.2. Fosters protectionism: Populist policies often lead to protectionist measures, contradicting regional integration goals.3. Encourages fragmentation: Nationalist sentiments can lead to regional fragmentation, weakening collective efforts.4. Threatens global governance: Militant nationalism challenges international institutions and norms, affecting regional and global stability.Other options:a. Differing visions of regionalism: While a challenge, differing visions can be addressed through dialogue and compromise.b. Disagreement among members: Disagreements are inevitable but can be managed through diplomatic efforts.d. Financial Crisis: Regional organizations can implement policies to mitigate financial crises' impact.Examples of nationalist and populist challenges to regionalism:1. Brexit (EU)2. Rise of nationalist parties in Europe (e.g., France, Germany, Italy)3. US-Mexico border wall and NAFTA renegotiation (North America)4. India's hesitation towards regional trade agreements (Asia)Regional organizations addressing these challenges:1. EU's efforts to address nationalist sentiments2. ASEAN's promotion of regional cooperation and dialogue3. African Union's initiatives for regional integration and cooperationTo overcome these challenges, regional organizations must:1. Foster inclusive dialogue2. Promote economic benefits of regionalism3. Encourage people-to-people exchanges4. Strengthen regional institutions and governanceSources:- Council on Foreign Relations- European Union Institute for Security Studies- Brookings Institution- World Economic Forum